1. Field of the Invention
This invention relates to polyimides which have a low coefficient of thermal expansion (CTE). More particularly, it relates to the preparation of an assembly of an article and a polyimide which resists dimensional change, delamination and debonding when exposed to changes in temperature.
2. Description of the Related Art
Polyimides have become widely used as high performance polymers as a result of their excellent thermal stability and toughness. However, polymers in general, including polyimides, have higher CTEs than metals, ceramics, and glasses. Lowering the CTE of polyimides would increase their usefulness for aerospace and electronic applications where dimensional stability is a requirement.
The CTEs of polyimides have been lowered in the past by linearizing the polymer molecular structure or by controlling the orientation of the polyimide film. Numata et al. (Polymer Engineering and Science, 28, (4), 906 (1988)) lowered the CTE by synthesizing a linear polyimide. By employing polyimides prepared from pyromellitic dianhydride (PMDA) or 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and aromatic diamines that contain only benzene or pyridine rings in para-positions without flexible linkages, they have synthesized polyimides with CTEs from 20-0.4 ppm/.degree.C. Numata and Miwa (Polymer, 30, (60), 1170 (1989)) found that the CTEs of uniaxially stretched polyimide films with rigid and flexible molecular chains were lower than their non-oriented counterparts.
By the present invention, an assembly of an article and a polyimide with a low CTE is prepared. The assembly resists dimensional change, delamination, and debonding when exposed to changes in temperature. The CTEs have been reduced by incorporating a metal ion-containing additive into a polyamic acid solution. St. Clair et al. (U.S. Pat. No. 4,284,461), Taylor et al. (U.S. Pat. No. 4,311,615) and Stoakley and St. Clair ("Lanthanide-Containing Polyimides" Recent Advances in Polyimide Science and Technology, W. D. Weber and M. R. Gupta, Eds., Society of Plastics Engineers, New York, 1987, pp 471-479) used these additives to alter the adhesive, electrical, and magnetic properties of polyimides.
Accordingly, it is the object of the present invention to prepare an assembly of an article and a polyimide which resists dimensional change, delamination, and debonding when exposed to temperature changes by forming a low CTE polyamic acid solution which is imidized.
Another object of the invention is to reduce the CTE of the polyimide by incorporating a metal ion-containing additive into the polyamic acid solution so it more closely matches the CTE of the article.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.